This invention relates to information displays of the general type illustrated in U.S. Pat. No. 3,562,938 to Salam granted Feb. 16, 1971. Such displays comprise a panel having a plurality of discrete light-transmitting areas arranged along transversely spaced upright columns and surrounded by a background which is preferably, but not essentially, opaque. The panel is normally backlighted and the desired display is viewed as light transmitted through the discrete areas. Circular disks are mounted for planar movement between the panel and a backing member. Each disk is individually movable between alternate stable positions, namely a first position in which the disk overlies the light-transmitting area associated thereto, and a transversely adjacent second position wherein it is clear of the light-transmitting area and to one corresponding side thereof. By arranging selected disks in one or the other of such positions, may desired lighted pattern can be achieved through the numerous light-transmitting areas, thereby producing the desired visual pattern on the viewed panel.
As described in U.S. Pat. No. 3,562,938, one method for controlling the disks is by use of a row of electromagnets arranged along an upright carriage which spans the height of the light-transmitting areas on the panel. Relative movement between the carriage and panel causes the panel to be swept in one direction across the width of the panel, thereby overlapping the respective first and second positions of each disk in a repetitive progression. By timing the activation of the individual electromagnets relative to such movement, each disk can be momentarily moved in relation to the panel or left stationary.
To use such a carriage to arrange the disks in a desired pattern, it is first necessary that every disk be in a known position before being encountered by the electromagnetic forces which control the display. According to the disclosure in U.S. Pat. No. 3,562,938, this is achieved by traversing the panel with all of the electromagnets in an energized state. This will draw all of the disks to a corresponding position. This is accomplished during return movement of the carriage in a direction opposite to the carriage movement when arranging the disks in a display.
Presetting the disks during return movement of the carriage has operational drawbacks. Most importantly, the proper magnetic coupling of the disks to the electromagnets on the carriage necessitates that the rate of speed of the carriage relative to the panel be limited. Excess speed might result in some disks not being reset. From a visual standpoint, such presetting requires that the lighted display be gradually blanked from one side to the other so that there is a progressive deactivation of the display. During this time, the portions of the display which have been reset are obviously not usable for communication purposes. In a constantly changing display, such as an airline schedule board, this full panel reset process requires a substantial percentage of the total time of display utilization. Since one advantage of the type of display to which this disclosure relates is its versatility and ability to be rapidly changed, the relatively slow full panel reset function is a negative operational function.
The present improvement was devised in an attempt to minimize the time required to reset the disks and substitute an alternative display on the panel. This is accomplished by doing both functions almost simultaneously in a rapid progression as the carriage moves in one direction across the panel.